This replacement HEPA filter can be used one of two ways. Use it as a replacement on a Dustless HEPA Vacuum that was factory certified and your vacuum will retain its certification, important when working under OSHS and NIOSH guidelines. The Micro Pre-filter is very economical and captures airborne particles down to 0.5 microns, amazingly close to the 0.3 micron level of the HEPA filter. That means the lower cost Micro Pre-filter captures the majority of dust, dirt and debris leaving the HEPA filter to capture only the finest particles.